JP2000002170A - Control device for internal combustion engine for natural gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always perform an excellent ignition timing control even when natural gas of different compositions is used by calculating a composition parameter of fuel according to air-fuel ratio controlled variable set based on an output of an air-fuel ratio detection means in a stationary operating state of an engine and correcting ignition timing according to this parameter. SOLUTION: When engine speed and absolute pressure within a suction pipe are within prescribed ranges and a vehicle is in a cruise state, an air-fuel ratio correction coefficient is calculated according to an output of an O2 sensor 16, an off idle average value and a cruise average value are calculated and the cruise average value is used as a composition parameter showing the composition of natural gas. A map is retrieved according to engine speed and absolute pressure within a suction pipe, basic ignition timing is calculated, a table is retrieved according to the cruise average value and a gas composition correction term is calculated. Continuously, a knocking correction term is calculated based on the gas composition correction term. The gas composition correction term and a knocking correction term are added to the basic ignition timing and ignition timing is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling an air-fuel ratio and an ignition timing of an air-fuel mixture supplied to an internal combustion engine using natural gas as a fuel, and more particularly to a control device which takes account of variations in the composition of natural gas. About things.

[0002]

2. Description of the Related Art In recent years, social demands for alternative fuels to petroleum have been increasing from the viewpoint of reduction of exhaust gas from automobiles, depletion of energy resources, and the like. It has been known.

In a control device for an internal combustion engine using gasoline as a fuel, an ultrasonic fuel property sensor is supplied with an ultrasonic fuel property sensor in order to cope with variations in characteristics (mainly volatility) of gasoline on the market. A device provided in the middle of a pipe to correct the amount of fuel injected into an intake pipe of an internal combustion engine in accordance with a detection value of this sensor has been conventionally known (Japanese Patent Application Laid-Open No. 8-17747). In the case of an internal combustion engine using natural gas as a fuel, a control device for controlling the internal combustion engine in consideration of variation in the composition of natural gas has not yet been proposed.

[0004]

Since the composition of natural gas has a greater variation than that of gasoline, in an internal combustion engine using natural gas as a fuel, optimum ignition timing and knocking at which a maximum output torque can be obtained occur. It has been experimentally confirmed that the ignition timing that tends to change considerably depends on the composition of the natural gas used.

The present invention has been made in view of this point, and appropriately controls an internal combustion engine using natural gas as a fuel.
It is an object of the present invention to provide a control device for a natural gas internal combustion engine that can always perform good ignition timing control even when natural gas having different compositions is used.

[0006]

In order to achieve the above object, an invention according to claim 1 is an air-fuel ratio detecting means provided in an exhaust system of an internal combustion engine using natural gas as fuel, and the air-fuel ratio detecting means is provided. Feedback control means for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the engine according to the output of the engine, and ignition timing control means for controlling the ignition timing according to the operating state of the engine. A controller configured to calculate a composition parameter indicating a composition of the fuel in accordance with an air-fuel ratio control amount used for the feedback in a steady operation state of the engine; and to control ignition in accordance with the composition parameter. Ignition timing correction means for correcting the timing.

[0007] According to this configuration, a composition parameter indicating the composition of fuel, that is, natural gas, is calculated according to the air-fuel ratio control amount set based on the output of the air-fuel ratio detecting means in a steady operation state of the engine. Since the ignition timing is corrected according to the calculated composition parameter, even when natural gas having a different composition is used, good ignition timing control can always be performed.

According to a second aspect of the present invention, in the control device for an internal combustion engine for natural gas according to the first aspect, the ignition timing correction means is configured to maximize the output of the engine according to the composition parameter. The ignition timing is corrected.

According to this configuration, the ignition timing is corrected so that the output of the engine is maximized in accordance with the composition parameter of the fuel being used. Therefore, even when natural gas having a different composition is used, the engine is always operated. Can be controlled to maximize the output of the ignition.

According to a third aspect of the present invention, in the control apparatus for an internal combustion engine for natural gas according to the first or second aspect, the ignition timing correction means prevents knocking of the engine according to the composition parameter. And correcting the ignition timing by the knocking correction term.

According to this configuration, a knock correction term for preventing engine knocking is calculated in accordance with the composition parameter, and the ignition timing is corrected by the knock correction term, so that natural gas having a different composition is used. Even in such a case, it is possible to control the ignition timing to an optimum value within a range where knocking does not occur.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a natural gas internal combustion engine (hereinafter, simply referred to as an “engine”) and a control device therefor according to an embodiment of the present invention, for example, in the middle of an intake pipe 2 of a four-cylinder engine 1. A throttle valve 3 is provided. The throttle valve 3 has a throttle valve opening (θT
H) The sensor 4 is connected, and outputs an electric signal corresponding to the opening degree of the throttle valve 3 and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each injection valve is electrically connected to the ECU 5. The valve opening time is controlled by a signal from the ECU 5. The fuel injection valve 6 is provided with a compressed natural gas (CNG: Compressed Na
A pressure regulator 21 for adjusting the pressure of the compressed natural gas supplied to the fuel injection valve 6 is provided in the middle of the fuel passage 20.

The spark plug 20 of each cylinder of the engine 1
The ignition timing is controlled by the ECU 5. On the other hand, an intake pipe absolute pressure (PBA) sensor 8 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. Further, an intake air temperature (TA) sensor 9 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5.

An engine water temperature (TW) sensor 10 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects an engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5. Engine speed (NE)
The sensor 11 and the cylinder identification (CYL) sensor 12 are mounted around a camshaft (not shown) of the engine 1 or around a crankshaft. The engine speed sensor 11 is the engine 1
A pulse (hereinafter referred to as a "TDC signal pulse") at a predetermined crank angle position every time the crankshaft rotates by 180 degrees, and the cylinder discriminating sensor 12 outputs a signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 5.

The three-way catalyst 14 is disposed in the exhaust pipe 13 of the engine 1 and purifies components such as HC, CO and NOx in the exhaust gas. On the upstream side of the three-way catalyst 14 of the exhaust pipe 13, an oxygen concentration sensor 16 (hereinafter referred to as "O2 sensor 16") as an air-fuel ratio detecting means is mounted. Is detected, and an electric signal corresponding to the detected value is output and supplied to the ECU 5.

The ECU 5 is connected to a vehicle speed sensor 19 for detecting a running speed (vehicle speed VP) of a vehicle on which the engine 1 is mounted, and a detection signal is supplied to the ECU 5.
The ECU 5 shapes input signal waveforms from various sensors,
An input circuit 5 having functions such as correcting a voltage level to a predetermined level and converting an analog signal value to a digital signal value.
a, a central processing unit (hereinafter referred to as “CPU”) 5b,
The storage unit 5c stores various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d that supplies a drive signal to the fuel injection valve 6, and the like. The storage unit 5c is backed up by the battery even when the ignition switch is turned off, and has a backup memory for retaining the stored contents.

Based on the various engine parameter signals described above, the CPU 5b performs various operations such as an air-fuel ratio feedback control region for performing air-fuel ratio control in accordance with the oxygen concentration in the exhaust gas and an open loop control region for not performing air-fuel ratio feedback control. The engine operation state is determined, and the fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated based on the following equation (1) according to the determined engine operation state. TOUT = TIM × KO2 × K1 + K2 (1) where TIM is a basic fuel amount, specifically, the fuel injection valve 6
The basic fuel injection time is determined by searching a TI map set according to the engine speed NE and the intake pipe absolute pressure PBA. The TI map indicates the engine speed NE.
In the operating state corresponding to the intake pipe absolute pressure PBA, the air-fuel ratio of the air-fuel mixture supplied to the engine is set to be substantially the stoichiometric air-fuel ratio with respect to a reference fuel (for example, natural gas of 100% methane). I have.

KO2 is an air-fuel ratio correction coefficient (hereinafter simply referred to as "correction coefficient"), which is obtained in accordance with the oxygen concentration in the exhaust gas detected by the O2 sensor 16 during the air-fuel ratio feedback control, and In the control region, the value is set to a value corresponding to each operation region.

K1 and K2 are other correction coefficients and correction variables calculated in accordance with various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to the engine operating condition. Is determined to be a predetermined value.

The CPU 5b further calculates the ignition timing θIG (indicated by the amount of advance from top dead center) by the following equation (2). θIG = θIGM + DIGMBT + DIGKNK (2)

Here, θIGM is the engine speed NE.
And a basic ignition timing determined by searching a θIG map according to the intake pipe absolute pressure PBA. The θIG map is
In the operating state corresponding to the engine speed NE and the intake pipe absolute pressure PBA, the reference fuel (for example, methane 1
(00% natural gas) is set to be the optimum ignition timing (MBT) at which the output torque of the engine 1 is maximized. DIGMBT and DIGKNK are an MBT correction term and a knock correction term that are set according to a composition parameter indicating the composition of the fuel, as described later.

The CPU 5b outputs a drive signal for driving the fuel injection valve 6 and the ignition plug 20 via the output circuit 5d based on the fuel injection time TOUT and the ignition timing θIG obtained as described above. 20.

FIG. 2 is a flowchart of a KO2 feedback control process for calculating the correction coefficient KO2 according to the output of the O2 sensor 16. This process is executed by the CPU 5b in synchronization with the generation of the TDC signal pulse.

In step S1, it is determined whether or not the previous air-fuel ratio control was an open loop control, and if not, it is determined whether or not the previous engine operating state was an idle state ( Step S
2) If it was in the idle state last time, it is determined whether or not it is also in the idle state this time (step S3). Here, whether the engine is in the idle state is determined by the engine speed NE.
And the throttle valve opening θTH.

As a result, the answer to step S2 is negative (N
If the answer is O), or if the answers of steps S2 and S3 are both affirmative (YES), that is, if the previous idle state was not established, or if the previous and current idle states are present, the process proceeds to step S4, and the previous idle state is executed. If the state is not the idle state this time, that is, if the state has shifted from the idle state to another operating state (hereinafter, referred to as “off-idle state”), step S1 described below is performed.
Proceed to 4.

In step S4, it is determined whether or not the magnitude relationship between the output level of the O2 sensor 16 and the reference value VREF has been inverted. If the average value is not inverted, while the average value calculation process of
The following integral control (I-term control) is executed.

In step S5, a process of adding the addition proportional term PR to the previously calculated KO2 value or subtracting the subtraction proportional term PL from the previously calculated KO2 value according to the magnitude relationship between the output level of the O2 sensor 16 and the reference value VREF. Execute In the following step S6, a limit check is performed for processing so that the calculated value of the correction coefficient KO2 falls within the range of the predetermined upper and lower limit values.

Next, in step S7, it is determined whether or not the engine is in an idle state. If the engine is in an idle state, an average idle value KREF0 is calculated (step S7).
8) While proceeding to step S11, if the vehicle is in the off-idle state, the average off-idle value KREF1 is calculated (step S9), and the cruise average value KREFCR is calculated.
S is calculated by the processing of FIG. 3 described later (step S1).
0), and proceed to step S11. Here, each average value KRE
Each of F0, KREF1, and KREFCRS is an average value of the correction coefficient KO2, and each of the average values KREF0, KREF
F1 and KREFCRS are calculated by the following equation (3). KREF (n) = CREF × KO2 / A + (A−CREF) × KREF (n−1) / A (3)

Here, (n) and (n-1) are added to indicate the current value and the previous value, respectively. A is a constant set to 10,000 (hexadecimal), for example, and CREF is a smoothing coefficient set to a value between 0 and A. The smoothing coefficient CREF may be set, for example, in two stages according to the engine coolant temperature TW. As KO2, a correction coefficient value immediately after execution of proportional control (that is, immediately after the output of the O2 sensor 16 is inverted and immediately after addition and subtraction of the proportional term) is used. In the following step S11, the calculated average values KREF0, KREF1, KREFCRS
Is performed, and the process ends.

On the other hand, if the previous time was the open loop control in step S1, it is determined whether or not the engine is in an idle state this time (step S12). If the engine is in an idle state, the correction coefficient KO2 is calculated as an idle average. Value KR
EF0 is set (step S13), and step S15 is set.
On the other hand, when it is not in the idle state, that is, when it is in the off-idle state, the correction coefficient KO2 is set to (off-idle average value KREF1 × CR) (step S).
14), and proceed to step S15. Here, the value CR is set to a value that improves the overall exhaust gas characteristics of the engine 1 according to the exhaust gas characteristics of the engine itself and the purification characteristics of the exhaust gas purification device.

If it is determined in step S3 that the engine is not in the idle state, that is, if the engine has shifted from the idle state to the off-idle state, step S14 is executed, and the process proceeds to step S15.

In step S15, the addition integral term IR or the subtraction integral term IL is added to the previous value of the correction coefficient KO2 according to the magnitude relationship between the O2 sensor output level and the reference value VREF and the count number of the TDC signal pulse. A subtraction process is performed, and the correction coefficient K calculated in the subsequent step S16 is calculated.
A limit check of O2 is performed, and this processing ends.

According to the processing of FIG. 2, the correction coefficient KO2 is calculated according to the output level of the O2 sensor 16, and
Average idle value KR when engine is idle
EF0 is calculated, and when in the off-idle state, the average off-idle value KREF1 and the average cruise value KREFC
RS is calculated. In addition, any average value is proportional term PR
Is calculated using the correction coefficient KO2 immediately after execution of the addition processing or the PL subtraction processing.

FIG. 3 is a flowchart of a process for calculating the cruise average value KREFFCRS executed in step S10 of FIG.

In step S101, the absolute value | KREF1-KREFCRS | of the deviation between the average off-idle value KREF1 and the average cruise value KREFCRS is set to a predetermined value DK.
It is determined whether it is smaller than RCRS and | KREF1-K
When REFCRS | <DKRCRS, the engine speed NE is set to the lower limit value NECRRFL and the upper limit value NECRR.
FH is determined (step S10).
2) When NECRRFL <NE <NECRRFH, it is determined whether or not the intake pipe absolute pressure PBA is between the lower limit PBCRRFL and the upper limit PBCRRFH (step S103), and PBCRRFL <PBA <PBCRH.
If it is RFH, it is determined whether or not a cruise flag FCRS indicating "1" that the vehicle is in a cruise state in which the vehicle travels at a substantially constant speed is "1" (step S104). As a result, when FCRS = 1,
The learning execution flag FCRSREF, which indicates that the cruise average value KREFFCRS should be newly calculated, that is, what should be learned, is set to "1" (step S10).
5) The cruise average value KREFCRS is calculated by the above equation (3) (step S106).

Next, a counter nCRS for counting the number of executions of step S106 is incremented by "1" (step S107), and it is determined whether or not the value is a predetermined value N (for example, 10) or more (step S108). n
When CRS <N, this process is immediately terminated, and nCR
When S ≧ N, the composition of the fuel in use is reflected on the cruise average value KREFCRS (the cruise average value KREFCRS correlated with the Wobbe index WI described later is obtained), that is, the fuel composition is detected. The composition detection flag FGC indicating that the operation has been performed is set to “1” (step S109), and the process ends.

The cruise flag FCRS is set in a cruise determination process shown in FIG. Further, a hysteresis may be provided in the determination in steps S101 to S103.

On the other hand, in step S102, NE ≧ NE
If CRRFH or NE ≦ NECRFLL, or if PBA ≧ PBCRRFH or PBA ≦ PBCRRFL in step S103, or if FCRS = 0 in step S104, the calculation of the cruise average value KREFCRS is not executed, and learning is performed. The execution flag FCRSREF is set to “0” (step S
111), this process ends.

In step S101, | KREF1-K
When REFCRS | ≧ DKRCRS, K is used to correct the cruise average value KREFCRS by the following equation (4).
Execute the REFCRS correction process (step S11).
0), this process ends. KREFCRS (n) = CREFCRS2 × KREF1 / A + (A-CREFCRS2) × KREFCRS (n−1) / A (4) where A is a constant set to, for example, 10000 (hexadecimal), and CREFCRS2 is 0 to A Is a smoothing coefficient set to a value between.

Here, the off-idle average value KREF1 is
If the engine 1 is in the off-idle state, the calculation is performed even if the vehicle is not in the cruise state. Therefore, the calculation frequency is higher than the calculation frequency of the cruise average value KREFFCRS. Therefore, the absolute value | KREF1-KR of the deviation between the off-idle average value KREF1 and the cruise average value KREFCRS
When EFCRS | is large, the cruise average value KREF
By correcting the CRS according to the off-idle average value KREF1, the learning accuracy of the cruise average value KREFFCRS can be improved.

According to the processing of FIG. 3, the cruise average value KR
The EFCRS is calculated when the engine speed NE and the intake pipe absolute pressure PBA are within predetermined ranges and the vehicle is in a cruise state, and the average off-idle value KREF is calculated.
When the absolute value of the deviation from 1 is large, the correction is made according to the off-idle average value KREF1. The cruise average value KREFFCRS calculated in this manner is used for correcting the ignition timing θIG as a parameter indicating the fuel composition when the composition detection flag FGC is “1” as described later.

The cruise average value KREFCRS calculated by the processing of FIG. 3 is stored in the backup memory and is retained even while the ignition switch is turned off. However, when the CNG tank 22 is filled with new fuel, it is reset to “1.0”. The counter nCRS is reset to "0" when the ignition switch is turned off, but the composition detection flag FGC
Is stored in the backup memory, and is reset to "0" when a new fuel is charged.

FIG. 4 is a flowchart of the cruise determination process, and this process is executed by the CPU 5b every predetermined time (for example, 80 msec).

First, it is determined whether or not the state of the engine 1 is in the start mode (step S31). As a result, when it is not in the start mode, it is determined whether or not the fail-safe processing of the vehicle speed sensor 19 and the like is being executed. Discrimination (step S3
2) As a result, when the fail-safe process is not being executed, the average value VPAVE of the vehicle speed VP is calculated by the following equation (5) (step S33). VPAVE (n) = (A−CCRS) × VP / A + CCRS × VPAVE (n−1) / A (5) where A is a constant set to, for example, 10000 (hexadecimal), and CCRS is 0 A smoothing coefficient set to a value between A.

Next, the average vehicle speed VPAVE is changed to the lower limit V
From CRSL (for example, 5 km / h) to the upper limit value VCRSH
(For example, 255 km / h) is determined (step S34).

As a result, when the engine 1 is in the start mode in step S31, when the field-safe process is being executed in step S32, or when VCRSL <VPAVE <VCRSH is not established in step S34, In any case, the process proceeds to step S42, and the down count timer tmDVCRS stores the predetermined time T.
DVCRS (for example, 1.25 sec) is set and started, then a predetermined time TCRS (for example, 2 sec) is set in the down count timer tmCRS and started (step S43), and the cruise flag FCRS is set to “0” ( Step S44), end this processing.

On the other hand, in step S34, VCRSL <
When VPAVE <VCRS holds, the timer tm
It is determined whether or not the value of DVCRS has reached "0" (step S35). If the value has not yet reached "0", this process is immediately terminated, while the value of the timer tmDVCRS has reached "0". At this time, a predetermined time TDVCRS is set in the timer tmDVCRS and started (step S36), and the fluctuation amount (vehicle speed fluctuation amount) DVCRS of the vehicle speed average value VPAVE is calculated (step S37). The vehicle speed fluctuation amount DVCRS is, for example, a current value and a previous value of the vehicle speed average value VPAVE (the stored value VPAVEB of the next step S38).
It is calculated based on the deviation from F).

Next, the stored value VPAVEBF is changed to the current V
The PAVE value is set (step S38), and the vehicle speed fluctuation amount D
VCRS is a predetermined value DVCRSLMT (for example, 0.8 km
/ H / sec) (step S39). As a result, DVCRS ≧ DVCRSLM
If it is T, the process proceeds to step S43, while the DV
When CRS <DVCRSLMT, the timer tmC
It is determined whether or not the value of RS has reached “0” (step S40). As a result, while tmCRS> 0, the process proceeds to step S44. When tmCRS = 0, it is determined that the vehicle is in a cruise state, and the cruise flag FCRS is set to “1” (step S41). Then, the present process ends.

According to this processing, the average value VPA of the vehicle speed VP
After the state in which VE is within the predetermined range is continued for a predetermined time TDVCRS, the state in which the fluctuation amount DVCRS of the average vehicle speed VPAVE is smaller than the predetermined value DVSCRLMT is changed to a predetermined time TC.
When RS is continued, it is determined that the vehicle is in a cruise state, and the cruise flag FCRS is set to “1”. Therefore, in step S106 in FIG. 3 described above, the cruise average value KREF is set only when the vehicle is running stably.
CRS learning is performed. Thereby, the reliability of the cruise average KREFFCRS can be increased.

The cruise flag FCRS indicates the vehicle speed V
Instead of detecting the fluctuation amount of P, the engine speed N
The amount of change in E may be detected and set to “1” when the state in which the amount of change is lower than the threshold has continued for a predetermined time or more.

FIG. 5 is a flowchart of a process for calculating the ignition timing θIG. This process is executed by the CPU 5b in synchronization with the generation of the TDC signal pulse. In this process,
The basic ignition timing θIGM is calculated according to the engine speed NE and the intake pipe absolute pressure PBA, and the MBT correction term DIGMBT and the knocking correction term DIGKNK are calculated according to a composition parameter indicating a value corresponding to the composition of natural gas. By correcting the basic ignition timing θIGM with these correction terms, the ignition timing θIG is calculated. The reason why the ignition timing is corrected in accordance with the composition of the natural gas is that the composition of the natural gas distributed on the market has a large variation as described below.

That is, the Wobbe Index WI (Wobbe Index) is known as an index indicating the calorific value per unit volume that changes depending on the composition of natural gas. The Wobbe Index WI of natural gas distributed in the market is 40-58
(MJ / m ³ ), and the Wobbe index WI and the optimum ignition timing MBT at which the output torque is maximized, as shown in FIG.
As the value of I increases, the optimum ignition timing MBT decreases, and the Wobbe index WI and the knocking ignition timing θKNK at which knocking occurs, as shown in FIG. 4B, increase as the Wobbe index WI increases. It has been experimentally confirmed that there is a relationship that the knocking ignition timing θKNK decreases. The Wobbe index WI is defined by the following equation (6). WI = HCV / SG ^1/2 (6) Here, HCV is a high calorific value of the natural gas (MJ / m
³ ), SG is the specific gravity of the natural gas.

Therefore, by correcting the ignition timing according to the Wobbe index WI of the natural gas used,
It is possible to set an ignition timing suitable for the natural gas, that is, an ignition timing at which a maximum torque is obtained in a range where knocking does not occur.

On the other hand, the correction coefficient KO2 and the Wobbe index WI obtained by executing the above-described air-fuel ratio feedback control in a steady operation state of the engine using natural gas as fuel are as shown in FIG. 8 (c). It has been experimentally confirmed that there is a relationship in which the correction coefficient KO2 decreases as the Wobbe index WI increases (theoretically, the two have an inversely proportional relationship).

Therefore, in the present embodiment, the cruise average value KREFCRS of the correction coefficient KO2 calculated by the processing of FIG. 3 is used as the composition parameter indicating the composition of the natural gas. This is because the correction coefficient KO2 calculated in the cruise state of the vehicle hardly includes a variation due to a change in the engine operation state, and is an air-fuel ratio correction coefficient obtained in a steady operation state of the engine.

Returning to FIG. 5, the details of a specific calculation process of the ignition timing θIG will be described. In step S51, θIG is set according to the engine speed NE and the intake pipe absolute pressure PBA.
The map is searched to calculate the basic ignition timing θIGM. θ
The IG map is set so that the optimum ignition timing (MBT) is obtained when a reference fuel (for example, natural gas of 100% methane) is used.

Next, it is determined whether or not the fuel composition flag FGC is "1" (step S52).
C = 0 and the composition of the fuel in use is the average cruise value K
When not fully reflected in REFCRS, MBT
Correction term DIGMBT and knocking correction term DIGKNK
Are set to "0" (step S55), and the process proceeds to step S56.

On the other hand, when FGC = 1, the DI shown in FIG.
The GMBT table is searched to find the MBT correction term DIGMB
T is calculated (step S53). The DIGMBT table indicates that when the cruise average value KREFCRS = 1.0, D
Assuming that IGMBT = 0, the correction term DIGMB increases as the KREFCRS value increases (as the Wobbe index WI decreases).
T is set to increase. Correction term DIGMB
When T takes a negative value, it corresponds to the retard correction. FIG.
The DIGMBT table of FIG. 8A corresponds to the relationship between the Wobbe index WI and the optimum ignition timing MBT shown in FIG.

In the following step S54, a knocking correction term DIGKNK is calculated by the following equation (7). DIGKNK = DIGKNKGC × KIGNE × KIGPBA (7) where DIGKNKGC is the cruise average value KREF
7 is a gas composition correction term calculated by searching the DIGKNKGC table shown in FIG. 6B according to CRS. DI
The GKNKGC table shows the cruise average value KREFCR
When S is greater than a predetermined value KREFX (eg, 0.95), the correction term DIGKNKGC is set to “0”, and KR
In the range of EFCRS <KREFX, the correction term DIGKNKGC is set to decrease as KREFCRS decreases. The DIGKNKGC table shown in FIG. 6B corresponds to the relationship between the Wobbe index WI and the knocking ignition timing θKNK shown in FIG. 8B.

KIGNE is an engine speed correction coefficient calculated by searching a KIGNE table shown in FIG. 6C according to the engine speed NE. KIGNE
The table shows that the engine speed NE is equal to the predetermined speed NE0.
(For example, 6000 rpm), the correction coefficient KIGNE is set to “0”. In the range of NE> NE0, the correction coefficient KIGNE increases as the engine speed NE increases.
NE is set to increase. Also, KIGP
BA is a load correction coefficient calculated by searching the KIGPBA table shown in FIG. 6D according to the intake pipe absolute pressure PBA. In the KIGPBA table, the correction coefficient KIGPBA is set to “0” in a range where the intake pipe absolute pressure PBA is lower than a predetermined pressure PBA0 (for example, 560 mmHg), and in a range of PBA> PBA0, the intake pipe absolute pressure PB is set.
The correction coefficient KIGPBA is set to increase as A increases.

In step S56, the MBT correction term DIGMBT and the knocking correction term DIGKNK are added to the basic ignition timing θIGM according to the equation (2).
The ignition timing θIG is calculated, and the process ends.

FIG. 7 shows the engine speed NE (> NE0).
Cruise average value KREFCRS and each correction term DIG in an operating state in which
It is a figure which shows the relationship with MBT and DIGKNK (broken line), and a solid line corresponds to the sum of both. In such an operating state, when the cruise average value KREFCRS is small, in other words, when fuel having a large Wobbe index WI is used, M
BT correction term DIGMBT and knock correction term DIGK
Both NK become negative values, and the ignition timing θIG is corrected in the retard direction. As a result, the optimal ignition timing can be set within a range where knocking does not occur.

According to the processing of FIG. 5, the ignition timing θIG is
Since the correction is made in accordance with the cruise average value KREFCRS as a parameter indicating the composition of the fuel in use, it is possible to control the ignition timing to be optimal for the fuel in use within a range in which knocking does not occur. As a result, it is possible to appropriately correct the variation in the composition of the natural gas used, and to obtain good operability.

In this embodiment, the processing in FIG. 2 corresponds to the feedback control means, step S51 in FIG. 5 corresponds to the ignition timing control means, the processing in FIG. 3 corresponds to the composition parameter calculation means, and the processing in FIG. Steps S53, S54, S56
Corresponds to ignition timing correction means. The correction based on the MBT correction term DIGMBT calculated in step S53 in FIG. 5 corresponds to correcting the ignition timing so that the output of the engine 1 is maximized, and the knocking correction calculated in step S54 in FIG. The correction by the term DIGKNK corresponds to correction for preventing knocking of the engine 1.

(Other Embodiments) The present invention is not limited to the above-described embodiment, and various modifications are possible.
For example, in the above embodiment, the cruise average value KRE
FCRS was used as a composition parameter indicating the composition of natural gas. The air-fuel ratio correction coefficient KO was calculated using the relationship shown in FIG.
2 may be converted to a Wobbe index WI, and the Wobbe index WI may be used as a composition parameter.

The knocking correction term DIGKNK is given by
The calculation may be performed by the following expression (7a) instead of the expression (7). DIGKNK = DIGKNKGC + DIGKNKNE + DIGKNKPBA (7a) Here, DIGKNKNE is an engine speed correction term set as shown in FIG. 9A according to the engine speed NE, and DIGKNKPBA is based on the absolute pressure PBA in the intake pipe. 7 is a load correction term set as shown in FIG.

Further, the occurrence of knocking may be detected by a knocking sensor or the like, and the knocking correction term DIGKNK may be corrected according to the detection result, thereby performing feedback correction of the ignition timing.

In the above-described embodiment, the cruise average value KREFCRS and the composition detection flag FGC are held in the backup memory, and when fuel is charged,
The cruise average value KREFCRS is reset to "1.0" instead of resetting to "1.0" and "0", respectively.
The smoothing coefficient CREF of the above equation (3) for calculating S is set within a predetermined period (period where nCRS <N) immediately after the filling.
The value may be set to a larger value than during the predetermined period (the contribution of the current value of the correction coefficient KO2 may be increased).

[0070]

As described above in detail, according to the first aspect of the present invention, the fuel is controlled in accordance with the air-fuel ratio control amount set based on the output of the air-fuel ratio detecting means in a steady operation state of the engine. That is, the composition parameter indicating the composition of the natural gas is calculated, and the ignition timing is corrected in accordance with the calculated composition parameter, so that even when using natural gas having a different composition, good ignition timing control is always performed. be able to.

According to the second aspect of the invention, since the ignition timing is corrected so that the output of the engine is maximized in accordance with the composition parameter of the fuel being used, natural gas having a different composition is used. Even in such a case, it is possible to always control the ignition timing so that the output of the engine becomes maximum.

According to the third aspect of the present invention, a knocking correction term for preventing engine knocking is calculated in accordance with the composition parameter, and the ignition timing is corrected by the knocking correction term. Even when natural gas is used, it is possible to control the ignition timing to an optimum value as long as knocking does not occur.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a process for calculating an air-fuel ratio correction coefficient (KO2).

FIG. 3 is a cruise average value (KREFC) of an air-fuel ratio correction coefficient.
14 is a flowchart of a process for calculating RS).

FIG. 4 is a flowchart of a process for determining a cruise state of the vehicle.

FIG. 5 is a flowchart of a process for calculating an ignition timing (θIG).

FIG. 6 is a diagram showing a table used in the processing of FIG. 5;

FIG. 7 is a diagram illustrating a correction term (DIGMBT, DIGKN) for the ignition timing.
It is a figure showing the example of setting of K).

FIG. 8: Wobbe index (WI) and optimum ignition timing (MB)
T), a diagram showing the relationship between knocking ignition timing (θKNK) and air-fuel ratio correction coefficient (KO2).

FIG. 9 is a diagram showing a table for calculating a knocking correction term.

[Explanation of symbols]

1 internal combustion engine 5 electronic control unit (feedback control means, ignition timing control means, fuel composition parameter calculation means,
(Ignition timing correction means) 6 fuel injection valve 13 exhaust pipe 16 oxygen concentration sensor (air-fuel ratio detection means) 19 vehicle speed sensor 20 spark plug

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Seiichi Hosokai 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor Atsushi Ide 1-4-1 Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. (reference) 3G022 AA00 CA03 DA02 FA03 FA04 FA06 GA00 GA01 GA05 GA07 GA08 GA19

Claims (3)

[Claims] 1. An air-fuel ratio detecting means provided in an exhaust system of an internal combustion engine using natural gas as fuel, and an air-fuel ratio of an air-fuel mixture supplied to the engine is feedback-controlled in accordance with an output of the air-fuel ratio detecting means. In a control device for a natural gas internal combustion engine having feedback control means and ignition timing control means for controlling ignition timing in accordance with an operation state of the engine, an air conditioner used for the feedback in a steady operation state of the engine. Natural gas for fuel gas, comprising: fuel composition parameter calculating means for calculating a composition parameter indicating the composition of the fuel according to a fuel ratio control amount; and ignition timing correction means for correcting an ignition timing according to the composition parameter. Control device for internal combustion engine. 2. The natural gas internal combustion engine according to claim 1, wherein the ignition timing correction means corrects the ignition timing so that the output of the engine becomes maximum according to the composition parameter. Control device. 3. The ignition timing correction means calculates a knock correction term for preventing knocking of the engine in accordance with the composition parameter, and corrects the ignition timing with the knock correction term. The control device for a natural gas internal combustion engine according to claim 1 or 2.